Generally the spring rates for coilovers are a fair bit higher than they would be for stock.
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But better damping doesn't necessarily mean a harsher ride.
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BC offer three options for spring rates.
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5/8kg seems the likely option.
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For a slightly easier ride 4/7kg, or 4/6kg may be preferable, though I'm not sure that BC offer custom spring rates like say, Tein do.
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I would generally want to reduce the difference between front and rear a bit.
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I went for 6/5kg from Tein for my AE86, but I had them made to spec.
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I don't know the stock spring rates but they will be low, like 2/3kg or some such.
http://www.bc-racing.co.uk/applications ... -ra-4.html